The invention provides a high-density floppy disk for use in data storage, wherein the substrate is a flexible metallic substrate.
Magnetic recording media such as floppy disks have been used for recording data used in computers for a number of years. As software has become more complex, the amount of information to be stored on magnetic storage media has increased dramatically. Floppy disks have previously been used to store this data. However, floppy disks are limited in the amount of information that they can store, and it is desirable to increase the storage capacity or density of floppy disks.
Non-uniform thermal expansion or contraction of the data disk limits the amount of data that can be placed on a floppy disk. Available data disks expand at different rates along different radii of the disk. The disk and its tracks assume an elliptical shape as the environment (such as temperature and humidity) changes, and the read/write head cannot follow the elliptically-shaped on the disk. Thus, tracks in which data is stored have to be wide so that the read/write head sweeps a circular path within a track and locates data despite eccentricities in the shape of the track caused by non-uniform thermal expansion of the disk.
Floppy disks are typically made by coating a polymeric substrate of a polyester such as Mylar(copyright) or polyethylene terephthalate with a magnetic material which records data received from a magnetic recording head. The polymeric material used to make the substrate is typically an oriented polymer that is stretched in one direction so that the long chain molecules of the polymer orient themselves in a particular direction. The long-chain molecules of the oriented polymer become oriented due to the way the substrate is manufactured. A thick sheet of the polymer is stretched longitudinally and is either held in place laterally or stretched laterally (but stretched less laterally than longitudinally) until the thickness of the sheet reaches the desired thickness. Because of this stretching in predominantly one direction, the long-chain polymer molecules orient themselves primarily in the direction in which the polymer sheet was pulled most.
These oriented polymers are sensitive to environmental e.g., temperature, and humidity changes. For example, as the temperature increases or decreases, the polymer expands or shrinks. The oriented polymer expands or shrinks at a different rate in the direction of orientation than it expands or shrinks in a direction perpendicular to the direction of orientation.
Because portions of the substrate expand or shrink at different rates, it is difficult to retrieve data from a particular location. Changes in temperature affect the location of the data, and consequently, a wider data track has to be provided so that the read/write head can locate the data despite the track having an eccentric shape. As a result of this, data cannot be packed too closely on a floppy disk, and lower storage capacities than what can be achieved result. As more storage capacity on a floppy disk is needed, it is increasingly important to provide a substrate that does not suffer the shrinkage and expansion that an oriented polymer such as PET suffers.
Further, it is necessary to limit the amount of expansion with change in temperature. As shown in Table 1, a polyester has a high coefficient of linear thermal expansion. It is desirable to limit the amount of linear expansion so that a data head can accurately locate data on a disk.
It is therefore an object of this invention to provide a high-density data recording medium with essentially uniform expansion and contraction in all directions across the medium, thereby providing it with greater dimensional stability.
It is another object of the invention to provide a floppy disk that has greater data storage capacity than is provided by currently-available floppy disks. Other objects and advantages are apparent from the discussion herein.
The invention provides a high-density data recording medium for use in a floppy disc, the invention provides a high-density floppy disk, and the invention also provides methods for making a high-density data recording medium and a high-density floppy disk.
In one embodiment of the invention, the invention comprises a high-density recording medium for use in a floppy disk. The high-density recording medium comprises a metallic substrate and a data recording layer, wherein the metallic substrate is a non-ferrous metallic substrate or a non-magnetic metallic substrate. The data recording layer can be, for example, a magnetic data-recording layer or a magneto-optical data recording layer. The metallic substrate is sufficiently thin that the substrate flexes when contacted by a data head of a floppy disk drive when the high-density recording medium is incorporated into a high-density floppy disk, but the metallic substrate has sufficient strength that the metallic substrate is not permanently deformed by this contact. The metallic substrate also has sufficient mechanical properties such as hardness for use as e.g. a recording medium for a floppy disk.
In another embodiment of the invention, the invention comprises a high-density recording medium which comprises a metallic substrate and a data recording layer, wherein the metallic substrate comprises a non-metallic core and a metallic layer. The metallic layer is a non-ferrous metallic material or a non-magnetic metallic material. The metallic layer has a sufficient thickness and strength to prevent the non-metallic core from expanding significantly more in one direction (e.g. the direction of orientation of polymer molecules in a polymeric core) than in another direction (e.g. a direction perpendicular to the direction of orientation of the polymer molecules).
The invention also provides a floppy disk comprising a casing and a high-density recording medium as described above.
The invention also provides methods for making a high-density recording medium. One such method comprises (a) providing a flexible, disk-shaped substrate made of a material which expands at substantially the same rate along all radii of the disk-shaped substrate with a change in temperature, and (b) placing a data recording layer over the disk-shaped substrate.
Among other factors, the invention is based on the technical finding that a floppy disk made using a metallic substrate as described herein has greater dimensional stability so that data tracks remain essentially circular or annular despite changes in temperature and humidity, so that tracks can be made narrower and more data can be placed on the surface of the floppy disk. These and other technical findings and advantages are apparent from the discussion herein.